Method of protecting magnesium with a coating of titanium



y 1961 F. E. DRUMMOND 2,982,017

METHOD OF PROTECTING MAGNESIUM WITH A COATING OF TITANIUM Original Filed May 22, 1953 IN V EN TOR.

F 0L5 0M E. DRUMMOND I M (g Attorneys United States METHOD F PROTECTING MAGNESIUM WITH A COATING OF TITANIUM Folsom E. Drummond, Washington, D.C., assigpor, by mesne assignments, to Union Carbide Corporation, .New York, N.Y., a corporation of New York Original application May 22, 1953, Ser. No. 356,697,

now Patent No. 2,746,134, dated May 22, 1956. Di vided and this application Aug. 15 l 95, '.S er. No.

3 Claims. c1. 29-410 'It has been proposed heretofore to produce magnesium .alloy' she'etscomprising a core ofmagnesium or magnesium alloy provided with a coating consisting of pure magnesium or a magnesium alloywhich is more resistant to corrosive attack than the core metal. Such duplex metals, however, have not been generally ;satisfactory because they possess the disadvantage thatatany point where the core or base metal is exposed in contact with the coating metal, as, for example, alonga cut edge of the sheet, or where the coating has .been perforated, an electrolytic type of corrosion is setup which causes a preferential attack on the base metal resulting in an impairment of its structural properties.

This preferential or selective corrosive attack on the core metal will occur when thecore metal has an electrode potential greater than that of the outer metal. Un der these conditions a voltaic action may be set up between the two metals' in contact with the corroding medium and the resultant electrolytic actiontends. to dissolve the core metal. This type of corrosive action seri-f ously restrictsthe use of magnesium and certain of the, magnesium alloys as a core or base metal, in .the fabrica tion of duplex metal articles. a

The preferred metalor alloy used is titanium,' zir;

conium or alloys thereof, wherein titanium or zirconium,

or both, are the chief constituents. Other metals of group IV of the periodic table of elements, e.g., hafnium,

thorium, etc. may be substituted for all or a part of the titanium or zirconium, the high melting point metals ofgroup IVA being preferred. The A sub-groupof group.

IV comprises the elements vtitanium, zirconium, hafnium andtho'rium, i

'Itis an object'of this invention to' provide a duplex metal article consisting of a'metal or alloy which cor atent .2 g by a sheath comprising said corrosion-resistant metall'or'.

metal alloy, and wherein there is provided a lightweight metal article having thestructural properties of the corn-1 bined metals or alloys. A magnesium sheet or article, is thus provided having improved corrosioneresistant properties over magnesium metal or its alloys. v

Briefly, the invention comprises a composite metal body, which may be in the formof a sheet, tube or rod or the like wherein the base metal or core. comprises magnesium metal or a suitable alloy thereof and the. sheath or covering layer of a corrosion-resistant metal, as its principal constituent. The sheath or .coveringlayer may constitute from about 8% to 60% of thev weight. of the composite metal sheet, rod or bar, butfor most. purposes the preferred proportion is about 19 to or less of the weight of the composite product. One method of making a bonded composite sheet 0;; rod is by coating the surface of the magnesium surface. to be sheathed with molten metal, e.g. spraying molten, metal such. a zinc, cadmium, or alloys thereof, and then applying thereto a sheet or layer of titanium orzirconium metal. The magnesium sheet and corrosion resistant sheet being superimposed one upon the otherwith the sprayed molten metal film at the interfacegher superimposed sheets being heated to a temperature;of

I, about 600 to 700 F. or above, but. below the melting;

point of the interface bonding metal. 1 The. superimposed; sheets while still hot, are passedone or more, times; between rolls adjusted to 'producea substantialreduction in the thickness of .thelcomposite sheet. There results.

H a magnesium base sheet having a sheathof corrosion-t resistant metal strongly bonded thereto.

Using crushed sponge titanium metal, which is. cheaper; than titanium alloy metals, a suitable bonding agent such as molten metal may be employed to form the composite product. In this method crushed and screened titaniumv sponge metal (300 mesh or finer) is distributed asa powdered layer over the cleaned surface of the magnesium or magnesium alloy sheet and bonded therewith. by the use of moltenzinc, cadmium or asuitable alloy: thereof, as described above. Where titanium; alloy-par ticles are used which have a sufiiciently lowsintering temperature, the same may be united to the magnesiummetalsurface by sintering. Titanium metal in apure state has a melting pointof around 1800 F;;, so that;

the lower melting. point of titanium alloy, as, aforemengtioned, is preferably used forsinteringpurposes;

Zirconiumfmetal, as produced by electrolysis of its; double alkali metal .fluoridesalt, or by reduction of the oxide with calcium metal, may be used. 'Hafniumrisa used associated with zrcom'um from which, if desired,

it may be separated by fractional crystallization .Qfitheg,

complex fluorides. Thorium metal may be prepared ',by the action of alkali metal on the halide, ,e-.g., thorium (9 9.5%) acetic 'acid),f 'and which is protected, against this corrosive action by being provided with a sheath coating or covering of the 'etals or alloys of titanium,

zirconium, hafnium and thorium. I a v 3 Another object of the invention is to provide a duplex,

metal arti cle in which the core or base metal is mag n'siumorniagnesium alloy which is enclosed in a pro: e.

Another object is to provide a corrosion-resistant du J plex metal'article in which magnesium or various mag-I nesium alloys may be used as the base, or core metal,

and wherein the surfacesof thecore metal are protected of "the class of metals above described" shoultl have 'atr.

chloride. 7 I a .The corrosioneresistant metals are amphoteric andi rodes readily '-(e.gwhen subjected to boiling glacial P"sses the wmmon charastsristiwf a n e mpotential of the magnesium with which they are alloyed: The reason why this particular-group should exhibit, this effectis not entirely clear, but probably-has some: relationship to their relative positionin: the periodic. table; Thesemetals'raise the-electrode potential-ofthe magnesium in varying degrees, depending, first, upon.v the particular metal or metals used and, second upon; the particular amounts which may "be .added'to' the? magnesium. The choiceof the proper ma'gnesium any: a ',:to be used as the coating material injcombination with any given magnesium metal base depends upon afprede-- termined knowledge of the electrode potential of the 5 base. metal in question. I

The coating magnesium aIIoyscontaining en or'mo electrode potential greater These d fferent potentials are readily measured in accordance with methods long known. in the art against a standard electrodes If the potential of the base metal s electro-negative with respect to the standard-electrode,- 1t1s notnecessarythat the coatingmetal be electro-posi t'ive with respect to the standard electrode, but only that 1t be less electro-negative than the base metal in order to be satisfactory for the purpose of my invention.

Therefore, throughout this specification and claims, where it is said that theelectrode potential of the coating metal should be higher 'thanthat of the base metal, it is meant that the coating metal should be more electro-positive with respect to the standard electrode than is ,the base metal. #Wh1le .no fixed potential ditferenceis required between the electrode potential of the basemetal and that the coating; metal, a substantial protection maybe given any basemetal by a coating metal of higher elec trode potential. It is generally desirable that there be a. relatively wide difference in the electrode. potential of the assaorr than that of the base metal.

known alloys possessing known combination of proper ties may be used, such as a magnesiumbase alloy com-.

prising 6 to 7% aluminum, and less than 1% zinc, the remainder being magnesium. Other magnesium-base alloys commercially available which may beuscd besides magnesium are alloys containing tin zinc (4%) and manganese (1% remainder magnesium. Also mag-- nesium metal containing 1 to 3% manganese, with or widiout tin. r .In the drawing:

Figure l is a. perspective view of a duplexarticleor sheet having a core 10 of magnesium metal and an outer covering orlayer 11 of titanium metal or alloy.

twotmetals, since it has been found that" with greater differences in potential. there usually occurs less attack on the base metal, and by suitableadjustment of the I potentialdifference it is possible to afford the basemetal complete protection for all practical purposes.

A convenient standard electroc'e for measuring the pofential, ditference mentionedmay be readily selected from 7 those nowin regular use for similar measurements. ,For" the purpose of this description of the invention, a calom'el electrodehas been selected as astandard. Inmeasuring the electrode potential in question, the magnesiumfmetal to be tested is made one element of an electrolytic cell;

the calomel is made the otherelernent. The electrolyte is a normal solution of sodium chloride-containing'0.3,

percent by weight of hydrogen peroxide. The circuit; ,is closedand the potential ditferenceof the elements is measured on a potentiometer.

, Titanium metal powder useful in practicing this invention may be obtained from any suitable source and produced by ditferent processes. One method of producing titanium metal is by the reduction of titanium .tetrachloride with magnesium. The resultant titanium metal is recovered in the form of a spongy mass which is crushed to produce metalparticlesof suitable sizefor incorporating into the coating compositiom Although a titanium alloy of aluminum and chromium alloy containing chiefly titanium.

Figure 2 is a view in cross-section, illustrating aduplex metal article in the form of a tube, and comprising a base metal 12 of iron, magnesium or the like with an inner layer or liner 13 consisting of titanium metal or Figure 3 is a cross-sectional view of showing two sheets of metal 14 and 15 being. rolled andreducedin thick ness while bonding the pair of metalsheets together, one of the sheets as at 14 being designated asmagnesiumand reference character 15 representing titanium, zirconiumor the like metal.

Figure 4 illustrates in perspective and sectioned, a;

solid rod having a core 160i magnesium having an outer protective layer 17 .of a suitable corrosion-re- .1; sistant metal.

spraying themetal thereon.

Figure 5 isan enlarged cross-sectional View of a nesium-base alloy sheet 18 having a layer 19 of titanium zirconium orthe like metahwhich may be applied by As an alternative method of resistant metal over magnesium metal surfaces. the same maybe deposited 'by' gaesous metal deposition. This may'be accomplished by' employing a heat-decomposable carbonyl orhydride or an equivalent gaseous, compound of the metal tobe'depo si tedand efiecting thedeposition as described in the US. patents to F. E. 'Drummond, see v for example Nos. 2,332,309 and 2.344 138.

In forming the duplex article of my invention, any of the known methods of forming such duplex metal articles may be used. One method which has been found is-set out in an example illustrating the invention, it will,

be understood that other alloys of titanium may be'employed. Titanium alloyed with up to 10% of other" metals,e.g. molybdenum, tungsten, nickel, yanadium copper or iron, are illustrative of alloys which may also 'cThe term corrosion-resistant metals, as used in the specification and claims, is intended to include the metals and their alloys of the IV group of the periodic table and mixtures of metal particles wherein the metals of this group constitute the major constituent.

The addition of one or more of the elements above described to the corrosion-resistant metalfor the purpose of forming the protective coating or alloy may be made and in any suitableamount necessary, to, attain the desired electrode potentials so long as other desirable properties of the magnesium itself are not materially im paired; and, likewise other elements not deleteriously affecting the desired potential properties and other desirable characteristics of the magnesium maybe added.

In generaLthe following amounts of the metals of the class above described best serve the general purposes of particularly useful is to roll together the coating alloy and the base alloy in sheet or slab form as illustrated in Figure 3. It is satisfactory to cast the base alloy in an ingot mold lined with the coating alloy. The article may then, if desired, be mechanicallyiworked as for example, by rolling or drawing or other suitable operation to. form the. particular type of :dup lex article desired,

such as sheenrod or other form. of material. The working with intermediate heating incident to such forming operations tends to improve the bondbetween the coating metal and the base metal. Duplex material may also be produced by. spraying, gas plating or the like so 7 as to provide the magnesium metal with anadherent coat? as castings are to be coated 1 1 L The duplex articles. of the invention m aybe provided ing of corrosion-resistant metal or alloy. This method may be used to advantage where irregular shapes such on any one or all exposed surfaces with lthe protective coating alloy, as for example are shown in Figures 1 and 2 of the drawing. Figure 1 shows a duplex article comit prising a base 1 of a magnesium metal providedon its this invention in producing the electrode potential desired 1 without materially impairing other-desirable properties of the magnesium metal;

.The base. or core metal, that is to say, the layer or bpdy of metal. from which the duplex metal article. of my invention derives its principal structural properties, may be any magnesium metal having the properties which ii a l ats bisiaisf hs .fi ll j r i r. ria t.

top and bottom surfaces with amagnesium alloy coatinlg. In Figure 2, a duplex metal article in tubular form comprising a base metal having an inner layer or coating of gtitanium metal This type of material is useful, for example, in the manufacture of pipes material tomagnesiurnmetal.

What is claimed is:

7 1. A method of, providinga metaljsheet composed .principallyof magnesium metalwith a protective coating of titanium metal, said method comprisingapplying to said magnesium metal a bonding layer of. molten metal applying the corrosion- I used to conduct a 1 5 selected from the group consisting of zinc, cadmium and alloys thereof, thereafter applying on the resultant bonding metal a layer of titanium sponge metal, and heating the titanium metal coated magnesium sheet to a temperature to sinter the titanium metal to said bonding metal layer, and provide a composite metal product.

2. A method of providing a metal sheet composed principally of magnesium metal with a protective coating of titanium metal, said method comprising spraying to said magnesium metal a bonding layer of molten metal selected from the group consisting of zinc, cadmium and alloys thereof, thereafter applying on the resultant bonding metal a layer of titanium sponge metal, and heating the titanium metal coated magnesium sheet to a temperature to sinter the titanium metal to said bonding metal layer, and provide a composite metal product.

3. A method of providing a metal sheet composed principally of magnesium metal with a protective coating 'of titanium metal, said method comprising applying to said magnesium metal a bonding layer of molten zinc metal, applying on the resultant bonding metal a layer of titanium sponge metal having a particle size approximating 300 mesh, and heating the resultant titanium metal coated magnesium sheet to a' temperature to sinter the titanium metal to said bonding layer of zinc and provide a composite metal product.

References Cited in the file of this patent UNITED STATES PATENTS 1,306,568 Weintraub June 10, 1919 1,709,781 De Boer et a1 Apr. 16, 1929 1,733,813 Marden et al. Oct. 29, 1929 2,100,258 Larson Nov. 27, 1937 2,301,332 Scheller Nov. 10, 1942 2,366,168 Bakarian Jan. 2, 1945 2,463,010 Almen Mar. 1, 1949 2,477,279 Anderson July 26, 1949 2,491,284 Sears Dec. 13, 1949 2,536,673 Widell. Jan. 2, 1951 2,588,421 Shepard Mar. 11, 1952 2,682,702 Fink July 6, 1954 2,685,124: Toulmin Aug. 3, 1954 2,694,653 Loonam Nov. 16, 1954 2,704,727 Pawlyk Mar. 22, 1955 2,711,973 Wainer et a1. June 28, 1955 2,713,196 Brown July 19, 1955 2,746,134 Drummond .a May 22, 1956 2,746,888 Ross ....'May 22, 1956 2,772,985 Wainer Dec. 4, 1956 

1. A METHOD OF PROVIDING A METAL SHEET COMPOSED PRINCIPALLY OF MAGNESIUM METAL WITH A PROTECTIVE COATING OF TITANIUM METAL, SAID METHOD COMPRISING APPLYING TO SAID MAGNESIUM METAL A BONDING LAYER OF MOLTEN METAL SELECTED FROM THE GROUP CONSISTING OF ZINC, CADMIUM AND ALLOYS THEREOF, THEREAFTER APPLYING ON THE RESULTANT BONDING METAL A LAYER OF TITANIUM SPONGE METAL, AND HEATING THE TITANIUM METAL COATED MAGNESIUM SHEET TO A TEMPERATURE TO SINTER THE TITANIUM METAL TO SAID BONDING METAL LAYER, AND PROVIDE A COMPOSITE METAL PRODUCT. 